1. Field of the Invention
This invention relates to a process for increasing the specific gravity of red mud produced as a waste product of the Bayer process for extraction of aluminium from bauxite, and the use of the products of such an improved process as a weighting agent in drilling slurries or fluids or as the solid phase of a slurry used to seal crevices and fissures exposed by drilling and excavation.
2. Description of the Prior Art
Red mud is a leaching residue from the Bayer process for producing alumina from bauxites, and is so named because of the red brown color caused by its iron oxide content. According to a paper by Gerhard Haake entitled "Red Mud--A Waste or a Valuable By-Product?" appearing in Neue Hutte, Vol. 33, pp. 424-429 (November 1988), the amount of red mud resulting from aluminum production is estimated to be 30-35 million tons annually. At present, most of the red mud is impounded in mud lakes or lagoons.
This, however, is not an ideal solution to the disposal of red mud. Mud lakes requires a significant amount of land because the solids settle at a very slow rate. Thus, it is not unusual to have a mud lake of several hundred acres associated with each Bayer process plant site, and the mud lake must be carefully maintained to minimize of contamination of nearby water sources. Even when the sites are carefully maintained, increasing pressure from environmental agencies and environmental groups require further efforts to minimize the amount of red mud which must be disposed in lagoons or ponds.
Accordingly, attempts have been made to find uses for red mud, and to recover as much as possible of the useful minerals therefrom. Haake reports that red mud treated with sulfuric or hydrochloric acid produces soluble sulfates of aluminum and iron which are used for flocculating or precipitating agents in the purification of water. A comprehensive review of the technology available for utilization of red mud waste is contained in Parekh and Goldberger, "Utilization of Red Bayer Process Muds: Problems and Possibilities" a paper delivered at the Proceedings of Sixth Mineral Waste Utilization Symposium, U.S. Bureau of Mines and ITT Res. Inst. (1978). That paper discloses among other things that red mud could possibly be used in construction block and as brick materials, as plastic and resin fillers, and as a lightweight aggregate material in the fabrication of lightweight, strong concrete.
Other investigators have focused their attention on recovery of useful compounds from red by various treatment processes. For example, U.S. Pat. No. 3,311,449 treats red mud slurry with gaseous sulfur dioxide to separate dissolved sodium compounds from solids or residue. Subsequent treatment with water permits its recovery of iron oxide and titanium oxide.
U.S. Pat. No. 4,668,485 discloses a similar process. According to the disclosure in that patent, red mud is digested with sulfur dioxide in the presence of water to dissolve soda aluminum and silica. Addition of heat selectively precipitates silica and produces a liquor containing soda and aluminum. Addition of lime to the liquor produces a caustic aluminate solution that may be returned to the Bayer process and permits recovery of calcium sulfite which can be calcined to regenerate lime and sulfur dioxide.
Still another process for separating useful compounds from red mud is described in U.S. Pat. No. 3,574,537 in which sulfur dioxide is passed into a solution of red mud and iron oxides are separated therefrom. Further treatment including heating the liquor in a vacuum evaporator helps recover sulfur dioxide and aluminum compounds.
Efforts to recover useful compounds from red mud have largely ignored the important benefits which can be obtained by treating the red muds to improve their physical characteristics and make the waste itself into useful products.